Multiband operation is understood to mean a method of operation which can operate to send and receive in multiple transmission and reception bands in the same transmission standard. Multimode operation is understood to mean a method in which the mobile radio device can operate in different transmission and reception bands in different mobile radio standards. Modern mobile radio devices are equipped for multiband and multimode operation and can send and receive in seven different communication systems, for example.
Furthermore, modern mobile radio devices may have further complementary reception devices, for example UHF transmitters/receivers, DVB-H (Digital Video Broadcast-Handheld) receivers, Bluetooth, WLAN (Wireless Local Area Network), WiMAX, GPS (Global Positioning System) and so on. Advantageously, transmission and reception devices are implemented on a single board for all of the wireless systems.
The complementary transmission and reception systems, which are not associated with a mobile radio communication system, are usually designed for continuous reception in their respective allocated reception band or are not synchronized to the transmission and reception bands of the communication systems. The reception can or is intended to be effected in parallel with the operation of a communication system. In this context, it is possible to use the same antenna for the complementary systems and the communication systems. However, in most cases a second antenna which matches the requirements of the respective complementary radio system is usual.
The close physical proximity of communication system and complementary radio means that there is a high level of coupling between the antenna signal (transmitted signal) from the mobile radio unit and the radio signal from the complementary radio. In this case, interference frequencies situated outside the transmission/reception bands of the communication systems can occur which, although they do not interfere with the communication, significantly impair the reception quality in a complementary radio system. In some cases, this problem can be solved by virtue of communication systems and complementary radios operating in different time slots. In most cases, however, this is not possible on account of a lack of synchronization between the signals or in the case of continuous operation of these signals (such as in the case of WCDMA and DVB-H). By way of example, the transmitter in an EGSM communication system can interfere with one or more of the complementary radio systems.
Although it is possible to filter out the fundamental frequency of the transmitted signal in the complementary radio system since the reception band of the complementary radio system and the transmission/reception bands of the communication systems are different, the transmitter additionally produces interference signals at frequencies which are situated in the reception band of the complementary radio and, for example, can be attributed to broadband noise from the power amplifier or to parasitic leakage signals from the transmission device.